Method of making hydrofluoric acid



April 10, 192s.

W. lJ. HARSHAW ET AL METHOD OF MAKING HYDROFLUORIC ACID Filed Feb. 19, 1925 p2.. s. 50 v.. E da m Vivl 8T m m 64. m wf @a @W3 PatenaeApffio, 1928.-

UNITED 's'i'AiIa-sA PATENT-orifice.

WILLIAM J. HARsHAw, or sHAxER HEIGHTS VILLAGE, AND CHARLES s. PARKE, or' CLEVELAND, OHIO, AssIGNORs 'ro'rHE HAR'sHAw, FULLER a. GOODWIN COMPANY, OF CLEVELAND, CHIC, A CORPORATION OF OHIO.

HETHOD OE MARIN@ HYLROELUORIO ACID.-

imputation mea rebmary is, 1925. semi Nc. 10,261'.

It has long been known that when iuor'- spar (calcium iiuoride, CaFZ) is caused to react with sulphuric acid, H2SO4, hydro uoric acid gas, HF, will be given off, leaving a residue of calcium sulphate, CaSO,l the reaction being expressed by the equa- 'tion The original method for commercially making hydroiuoric acid by the foregoing process, and one still used to a considerable ex- .moved from the pot or pan and the residue,

which is in the form of a vhard solid mass, is removed preparatory to the introductionl of a fresh charge.

In the so-called Naugatuck process, provision. is made for the agitation of the materials in a potstill of thecharacter just described so as to stir and break up the mass during the heating Operation.

In place of a potstill, it has also been proposed to employ a stationary covered trough that constitutes in effect an elongated still,

such trough being slightly inclined and a` revolving 'shaft provided with radial arms extending lengthwise thereof, whereby'the material introduced at one end is continuously stirred and intermixed and at the same time carried gradually towards the other end. The trough is of course suitably heated so that the material in its passage therethrough may be brought to the reacting temperature. This 'last described process is a continuous one in contradistinction to the potstill operation and as an obvious adaptation of such process, it has also been pro osed to use an inclined 'revolving still/ of amilar ty e through which the material is continuous ypa'ssed, such material being continue until the material is lentirely used 10o agitated incidentally to the rotation of the I l l.

still. v 4

All of the foregoing methods have certain serious objections among which may be named the necessity that the iuorspar be, of

a relativelyhigh degree of purity, e. g. the so-called acid grade must run at a content of 98 'per cent of calcium 'uoride and' not more than 1 per cent of silica or of carbonate of lime. It is also necessary to the successful operation of any of the foregoing processes that the iiuorspar be very finely'- ground, if the reaction is to be carried through withl any degree of completeness, it being notedthat the agitation provided for in certain of the processes rei'erred'to` above has merely as its object to break up the mass of the reacting materials and avoid the` formation of the hard cakeby the calcium sulphate produced as a result ofthe reaction.

Not only is the fine grinding of the fluorspar :inexpensive operation, because of the hardness of the material, but when 'such finely ground material is brought in contact with the sulphuric acid, vunless the application of the heat bel carefully regulated, even the small ,percentage of carbonate of lime presentA in acid grade material Iwill result in excessive generation of carbon dioxide dur- 4 ing` the initial stage of the operation.

We have discovered that most, if not all, of the foregoing difiiculties can be successfully overcome by the utilization, in a suitably designed apparatus, of uiiground'v tluorspar, 1. e. raw material tliat has been simply crushed to fragments measuring from onehalf inch or even three-fourths inch in size down, if provision be made for comminuting the raw material in this form while the 'i u All tendency'to cake is obviously avoided) and' at the same time it becomes possible to use -relatively impure fluorspar, such as the grade knownv as fluxing spar in which the carbonate of lime'runs as hi has 10 per cent; this for the reason that t e acid can react only gradually on the carbonatefthus present, i. e. as the fragments of the spar are reduced in size by the grinding action, and there is accordingly at no time any dangerous excess of carbon dioxide given off.

To the accomplishment of the foregoing and related Yends, the invention, then, consists of the ste s and means hereinafter fully described andp particularly pointed outin the claims, the annexed drawing and the following description setting forth in detail certain means and one mode of carrying out the invention, such disclosed means and mode illustratin however, but one of various 'ways in whic the principle of the invention may be used.

Fig. 1 isl a longitudinal axial section of a retort designed for carrying out our present improved method or process; Fig. 2 is a broken front elevation of such retort, viewing the same as from the right in Fig. 1; and Fig. 3 is partly a transverse section and partly an elevation of the eduction or gas discharge pipe and the special support provided therefor.

As indicated above, in general the construction of our improvedretort follows the lines of the ordinary ball mill. Thus, as shown in Fig. 1, it consists of acylindrical shell 1 suitably closed by heads 2 and `3 at its respective ends. These heads rest on rollers 4 and 5., respectively,A which are so disposed as to support the retort in an inlclined position within Athe furnace chamer 6. y

The head 2 at thev lower end of the retort Lis rovided with a. central opening or manho e 7 i to which is fitted a removable cover 8, so that a batchv of fresh material can be introducedl into the retort through such opening when desired and subsequently removedvl when spent. To facilitate such removal, a series of radial ns or lifting plates 9 is secured in the corner of the retort between head 2 and cylindrical wall 1 adjacent opening 7, so' that when the cover is removed and a trough or scoop inserted through such opening, the material will be raised b these p ates and dro ped onto such troug until the retort is su stantially empty.

For the purpose of rotating the retort, an annular gear 10 is attached to the other head 3, such gear meshing with a inion 11 on a drive shaft 12, as need not e further explained. i

The gases generated during the operation of the retort are also removed through an tral opening in said head 3 so as to project a short distance withinl the retort. Owing to the highly corrosive character of hydrofiuoric 'acld gas, it is necessary that the joint between ,the pipe 'and the head 3 be very carefully sealed. vW'e have foundthat much more satisfactoryresults are obtainable by journaling saidpipe in the head than by fixing ,the pipe to' the latter in the form of a hollow trunnion for it is practically imposfsible in aretort ofany sizeto so mount the same onits roller supports as not to subject this pipe to acertain amount of weaving action. The exteriorly projecting portion of the pipe is accordingly resiliently supported as by means of a transversely disposed leaf spring 14 secured at its midpoint thereto, as Shown in Fig. 3; while the inner end of the pipe is journaled in a bronze bushing 15, fitted in thev central opening in head 3, and i's surrounded for some distance be ond the outer face of the head with a stu ing box 16 and stuffing gland 17. This gland serves to retain in the `stuffing box and around the enclosed portion of the pipe a suitable body of lubricating material which constitutes an effective se`al against Athe escape of gas and at the same time, by virtue of the flexible support provided for the pipe, no special wear is imposed o n the gland or bushing 15, the pilpe being free to accommodate itself to any s ight shifting movementgproduced by the rotation ofthe retort. The outer end of the pipe ,is flanged tovpermit its connection with an' extension 20 that leads to a suitable condenser or absorber,(nt shown).

In utilizing the foregoing retort, as previously indicated, we introduce along with the raw material, consisting of crushed luorspar, a quantityof iron balls 21 or irregular pieces or scraps of iron, since the shape of these is not important as affecting the results we obtain, althoughballs are preferable since theyv are less wearing on the walls of the retort. A s previously indica-ted, the fiuorspar need not be ground but merely crushed and fragments as large as one-half inch or three-fourths inch are not objectionable. The size of the iron balls ma similarly vary widely, e. g. from one incisi7 to five inches in diameter. A batch of the crushed fluorspar is simpl shoveled through iis opening 7 until a layer o desired thickness,

for instance as indicated by dotted line 22 vm Fig. 1 is formed,'and then a charge of sulphuric acid, equivalent to the luorspar, is run into the retort, it being understood that the iron balls will be introduced at the same time. Thereupon the cover 8 is eplaced and the retort slowly revolved while its temperature is slowly raisedby proper control of furnace 6.

While the action of the iron balls in di-`-` rectly reducing the original iluorspar frageduction pipe 13 that extends through a cen# ments is practlcally nil due to the hardness 130 of the fluorspar, the layer of calciumv sulphate that is formed .in such fragments by the reaction of the sulphuric acid therewit is relatively soft and is easily rubbed off. Fresh surfaces are being thus constantly exposed to the action of the acid and the operation is brought to a stage of completion simultaneously with the final reduction of these fragments. Thereupon the spent residue is removed in the manner already describedland a fresh batch of crushed fluorspar -with the proper amount of acid is introdced into the retort.

While the operation, as just noted, is discontinuous with a consequent variation in the rate at which the hydrofluoric acid gas is generated, the advantages obtained considerably outweigh any disadvantage that might be thought to attach to such discontinuous operation. Not only may a less expensive grade of fluorspar be utilized, but

the pre aration of such material by omitting the di cult grinding thereof is very muchless costly. At the same time a relatively smaller condenser for the hydrofiuoric acid gas will sufiic`e than with the ordinary potstill, for example, since even at the initial stage of the operation there is no such excessive generation of the gas as when finely ground material after being intermixed with the sulphuric acid is brought to the reacting temperature. Moreover, the carbon dioxide gas that results from the reaction of such acid with the calcium carbonate present is likewise given off slowly and any tendency for the mixture to foam is avoided.

By utilizing a fluxingspar with a high enough content of silica or by purposely adding silica in the form of sand, or equivalent siliceous material capable of reacting with the acids present, we may make fluosilicic acid, HzSiF, directly instead of hydrofiuoric acid.

Other modes of applying the principle of our invention may be em loyed instead -of the one explained, change eing made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

We therefore particularly point out and distinctly claim as our invention:

1. A'method of making hydrofluoric acid, which includes heating a mixture of a fluoride and an acid capable of reacting therewith to free such hydrofluoric4 acid, such fluoride being in broken, fragmentary, in contradistinction to ground, form; and removing sulphate coating from the surface of the fluoride fragments to allow further action.

2. A method of making hydrofluoric acid, which includes heating a mixture of a fluoride and an acid capable of reactin therewith to free such hydrofiuoric acid such fluoride being in broken, fragmentary, in contradistinction to ground, form; and rubbing ofi' sulphate coating from the surface of the fluoride fragments by the abrasive action of relatively hard bodies. l

3. A method of making hydrofluoric acid, which includes heating a mixture of a fluoride and an acid capable of reacting therewith to free such hydroiluoric acid such fluoride being in broken, fragmentary, in contradistinction to round, form; and when sulphate coating orms on the fluoride fragments, rubbing off such coating by the abrasive action of iron balls.

4. The method of making hydrofluoric acid, which consists in placing a batch composed of fiuorspar intermixed with sulphuric acid in a rotary retort; such fiuors ar being in broken, fragmentary, in contradistinction to ground, form; and a quantity of relatively hard bodies substantiall unaffected by such acid being included with7 the batch; heating said retort; and rotating the same and rubbing ofi sulphate coating from said fluorspar fra ments'as the reaction proceeds.

igned by us this 9th day of February, 

